It'll be an episodic side-scrolling platformer in the style of the first three classic Sonic games. It's not clear whether further episodes will be part of an update, or new games in themselves.
It's a sign of the iPhone's increasing dominance of the low-cost downloadable game market that it's getting first dibs on Sega's flagship platformer. It's already offering a serious alternative to the Nintendo DS and Sony PSP.
Work on the latest adventure of the spiky speedster started in 2009 under the codename Project Needlemouse. It was due for release earlier this year, but was held back to allow for more development.
Sega has already released a straight port of Sonic the Hedgehog and its sequel Sonic 2 to the App Store, in a series of old favourites transferred to the platform. Ancient Sega Megadrive games such as Golden Axe and Streets of Rage have met with varying degrees of nostalgic fondness. That the peerless racing beat 'em up Road Rash remains unreleased is a crying shame, in Crave's humble opinion.
Sonic 4 on the iPhone and iPod touch will be the same as the console versions, and controlled using a virtual d-pad or tilt and touch through the built-in accelerometer, according to toucharcade.com. Zones already known to be in the game so far are Splash Hill, the Lost Labyrinth and Casino Street.
Our sister site GameSpot spoke to Sega about the game at this year's E3, and in the video below you can see gameplay footage. Sonic has his signature speed and spin dash, but you'll also be able to hit enemies with a homing attack.
The game looks pretty impressive, with an emphasis on the original's perfect blend of blistering speed and platform puzzles. The first two Sonic games for iPhone and iPod touch were gorgeous and went at a fair old pelt, especially on the iPhone 4. No price details have been released yet, but they're likely to be cheaper than the downloadable console versions.